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Hey, Win! CCFL Inverter "self-learning" resonant frequency?

Discussion in 'Electronic Design' started by Jim Thompson, Nov 30, 2005.

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  1. Jim Thompson

    Jim Thompson Guest


    What do you know about CCFL inverters that claim "self-learning" of
    the transformer resonant frequency?


    ...Jim Thompson
  2. Fred Bartoli

    Fred Bartoli Guest

    Yes, how do they have the capacity to induce such a frequency?
  3. Joerg

    Joerg Guest

    Hello Jim,
    I am not Win and also not the expert on this but AFAIK the frequency is
    swept during start-up and upon strike is being locked into current maximum.

    However, I am only familiar with series resonant conversion and that's
    how it is often done there, in cases where max power transfer is desired
    instead of regulation. When regulating it is customary to slide up and
    down the lower frequency slope (with SRCs).

    If you are thinking about doing this in a chip, the method might be
    patent protected for CCFL. Not sure but a quick Google found this one:

    Regards, Joerg
  4. Jim Thompson wrote...
    That they've been listening to too much Rush Limbaugh?
  5. Jim Thompson wrote...
    Getting involved in patent cases again? I see a patent
    application "High-efficiency adaptive dc/ac converter,"
    is that the one? "... the circuit is self-learning
    and is adapted to determine the optimum operating
    frequency for the circuit with a given load"
  6. I'd dither, synchronously demodulate and integrate.

    Best regards,
    Spehro Pefhany
  7. Jim Thompson

    Jim Thompson Guest

    There are three patents, actually ;-)

    Already scheduled to court.

    Just poking around to see what's in the prior art.

    ...Jim Thompson
  8. Jim Thompson

    Jim Thompson Guest

    Who he ?:)

    ...Jim Thompson
  9. Jim Thompson wrote...
    I know about US6259615 and US6396722, what's the third?
    Same guy, Yung-Lin Lin? All dating to Nov 9, 1999?
  10. Jim Thompson

    Jim Thompson Guest

    And US6804129 B2, taking note of "Other Publications" on the first
    page ;-)

    ...Jim Thompson
  11. Joerg

    Joerg Guest

    Hello Jim,
    Doesn't the common oscillator count? After all it 'self-learns' the
    resonance of the LC circuit connected to it :-D

    That would put prior art back into the days of Heinrich Rudolph Hertz
    who passed away in 1894. As for switch mode controllers a frequency
    adaptive scheme was easily done with chips such as Unitrode's UC3860.
    Those are really old as well.

    Regards, Joerg
  12. Jim Thompson

    Jim Thompson Guest

    Thanks, Joerg! That's the kind of lead I'm looking for... really old
    prior art.

    I'm seeing an awful lot of issued patents these days that would
    indicate that the examiners aren't doing proper prior art searches...
    issuing patents on stuff us old farts knew about when we were kids ;-)

    ...Jim Thompson
  13. Guest

    Have a look at Baxandall's Class-D oscillator

    Baxandall, P.J, Proc I.E.E 106, B, page 748 (1959)

    The oscillator self-oscillates at the transformer resonant frequency.

    Jim William's used it in his classic application notes on CCFL drivers

    though he calls it a Royer inverter, which is pretty strange for a
    variety of reasons (Fred Bloggs begged to differ in our little spat on
    the 29th July 2002).

    Baxandall didn't develop the circuit explicitly to drive CCFLs - he
    needed to generate high voltages for other purposes - but it was fairly
    clearly intended to deal with the relatively high winding capacitances
    of transformers with a high step-up ratio.

    Pity that Jim has got me kill-filed - he'll never read this ...
  14. Joel Kolstad

    Joel Kolstad Guest

    As far as I can tell, while the patent office may well not be doing as much of
    a prior search as they should, these days every Tom, Dick, and Harry who comes
    up with a circuit that wasn't on one of their college homework assignments
    figures it ought to be patentable and the business people running many
    companies will do nothing but encourage them to do so -- prior art be damned.
  15. wrote...
    The immediate issue isn't to find a workaround, it's to find
    a way to invalidate a patent whose owners assert infringement
    by products using their patented scheme. Sadly, despite even
    good evidence of obviousness, it's very hard to get a jury to
    overturn a patent that enjoys a good presumption of validity,
    having passed careful review by patent examiners --- Who are
    amateur jurors to overturn a patent professional? To succeed
    one has to find something serous, like real evidence of fraud
    (applicant intentionally didn't mention significant prior art),
    or gross incompetence (the examiner failed to find or respect
    significant prior art), that forces the jury to feel compelled
    to over-rule the examiner.

    In other words, one must find EXACT instances of prior art.

    Either that, or the expert witness and defense lawyer (and his
    entire team) need to have *extraordinary* skill with the jury,
    so the jury feels the patent owner is a skank, and are looking
    for good excuses to do the right thing as citizens, and overturn
    his patent. That doesn't happen very often.
  16. One of the reasons I'm so depressed about patents lately is that whenever I
    go looking at patents to figure out whether I'm going to be sued for some
    obvious idea I've used, I see all kinds of other obvious things being
    patented. And I'm anything but a clever engineer, as Fred Bloggs has
    correctly observed on occasion, so if something's obvious to me it's just
    absurd that it's patented.

    Here's an example, patent 6,372,976, filed in 1998 and granted in 2002. "A
    pickup for an electric guitar includes a housing made to fill an existing
    cavity in an electric guitar body originally used for a dual-coil humbucking
    pickup. The pickup also has a single pickup coil mounted in the housing."

    In other words: they've patented the idea of putting something small into an
    enclosure, so that it fits a bigger existing hole.

    Is it conceivable that solving this problem took an engineer more than 30 or
    40 seconds of careful thought? Is it even conceivable that anyone could
    come up with a more obvious solution to the problem?

    I suppose now if I patent the idea of stuffing Kleenex into the end of
    hand-me-down shoes to make them fit, I'll have to cite this patent as prior
  17. In that case perhaps look at the spark gap transmitters
    developed by Marconi or Poulsen. AFAIR they used the negative
    resistance of an arc in association with a self-tuned LC tank.
  18. Fred Bartoli

    Fred Bartoli Guest

    Plus a spark gap arc is a kind of CCFL, no?
  19. Sort of. It's a discharge lamp, which could become an
    actual arc if the current was allowed to rise too high.
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